Ebbers argued in court papers that the trial judge improperly allowed prosecutors to use testimony from witnesses who had been given immunity, but denied immunity to potential defense witnesses.

The judge also instructed jurors that they could find Ebbers guilty if they believed he suspected a crime was being committed but intentionally looked the other way.

A federal appeals court upheld the conviction last year, acknowledging that Ebbers' sentence for a white-collar crime was longer than sentences routinely imposed by many states for violent crimes. The 2nd U.S. Circuit Court of Appeals said Ebbers' actions to hide WorldCom's financial problems were substantial, and had cost investors dearly.

Ebbers was convicted for his role in the massive fraud that drove Clinton, Miss.-based WorldCom into bankruptcy in 2002.

Investigators uncovered $11 billion in fraud at WorldCom Inc., much of it because accountants were classifying regular expenses as long-term capital expenditures. The company re-emerged under the name MCI. Verizon (VZ) later bought MCI.

In 2005, the court unanimously threw out the conviction of the Arthur Andersen accounting firm for destroying Enron Corp.-related documents because the jury instructions were too broad.